Smoke and gas detection and alarm apparatus

ABSTRACT

An improved Taguchi Gas Sensor type detection and alarm system for smoke, gases or the like, which is particularly adapted for use in environments where the only available source of electrical operating power is an ordinary storage battery, is provided and employs an electrical oscillator coupled with the storage battery for providing both the low voltage high current electrical power required for activating the Taguchi Gas Sensor and an audio frequency output signal for operating an audible warning component of the system when the sensor has detected the presence of smoke, gases or the like. The electrical circuit coupling the audio warning component with the output of the oscillator includes an electrically controlled switching device responsive to detection of existence of a hazardous condition by the sensor; and such circuit also includes in the coupling between the sensor and the switching device, means for providing a suitable delay prior to operation of the switching device to prevent the generation of false warning signals during warm-up or &#39;&#39;&#39;&#39;purging&#39;&#39;&#39;&#39; of the sensor upon start-up of the system. The preferred embodiment of the invention further provides an auxiliary oscillator of substantially lower frequency than the first mentioned oscillator which is coupled with the latter to provide a distinctive dual tone warning signal alternating between different audio frequencies. The improved apparatus is adapted for implementation by means of integrated circuit modules for the primary active electronic components.

United States Patent [191 Aker 14 1 Jan. 14, 1975 SMOKE AND GASDETECTION AND ALARM APPARATUS John L. Aker, Chanute, Kans.

Donald E. Funck, Overland Park, Kans.

Filed: Dec. 26, 1973 Appl. No.: 428,094

lnventor:

Assignee:

[52] US. Cl 340/237 R, 331/65, 340/237 S, 340/309.1, 340/384 E Int. Cl.G08b 21/00, G08b 3/00 Field of Search 340/237, 384 E, 309.1

References Cited UNITED STATES PATENTS Primary Examiner]ohn W. CaldwellAssistant Examiner-Daniel Myer Attorney, Agent, or Firm-Schmidt,Johnson, Hovey & Williams [57] ABSTRACT An improved Taguchi Gas Sensortype detection and alarm system for smoke, gases or the like, which isparticularly adapted for use in environments where the only availablesource of electrical operating power is an ordinary storage battery, isprovided and employs an electrical oscillator coupled with the storagebattery for providing both the low voltage high current electrical powerrequired for activating the Taguchi Gas Sensor and an audio frequencyoutput signal for operating an audible warning component of the systemwhen the sensor has detected the presence of smoke, gases or the like.The electrical circuit coupling the audio warning component with theoutput of the oscillator includes an electrically controlled switchingdevice responsive to detection of existence of a hazardous condition bythe sensor; and such circuit also includes in the coupling between thesensor and the switching device, means for providing a suitable delayprior to operation of the switching device to prevent the generation offalse warning signals during warm-up or purging of the sensor uponstart-up of the system. The preferred embodiment of the inventionfurther provides an auxiliary oscillator of substantially lowerfrequency than the first mentioned oscillator which is coupled with thelatter to provide a distinctive dual tone warning signal alternatingbetween different audio frequencies. The improved apparatus is adaptedfor implementation by means of integrated circuit modules for theprimary active electronic components.

12 Claims, 1 Drawing Figure meg SMOKE AND GAS DETECTION 'AND ALARMAPPARATUS This invention relates to detection and alarm apparatus foruse in detecting and providing a warning of the presence of smoke, gasesor the like such as would indicate the commencement of a fire or otherpotentially hazardous condition. More particularly, the inventionprovides improvements for such apparatus, especially with respect toproviding such apparatus that is adaptable for practical use inenvironments such as motor homes, wherein the only available source ofcontinuous electrical power may be from a battery.

One of the most reliable of the available instrumentalities fordetecting the presence of smoke or unburned hydrocarbon gases iscommercially known as the Taguchi Gas Sensor. Such sensors are extremelysensitive in the detection of smoke, gases or the like and are employedin various previous fire detection and prevention systems for use innormal commercial and domestic environments in which an essentiallyunlimited supply of electrical energizing power therefor is availablefrom the regular electrical supply lines. However, Taguchi Gas Sensorsare characterized by their requirement of electrical activating power ofrelatively high current at low voltage, typically around 0.6 Ampere at 1Volt, AC. or DC, which heretofore has been regarded as rendering theiruse impractical in environments where the only available power sourcemay be a battery whose charge would be quickly dissipated by such aheavy current drain during continuous operation of the hazard monitoringsystem. Similarly, the means employed in conventional systems forproviding a warning of the detection of a hazard condition normallyimposes additional, and often substantial, electrical power requirementson the supply source. Additionally, conventional systems of this generaltype are commonly subject to various other limitations and disadvantagessuch as susceptibility to false warning signals, inadequacy in providinga positive and distinctive type of warning signal, a tendency towardeither limited reliability or undue complexity and space requirements,etc.

It is, therefore, the primary object of this invention to overcome theforegoing and other limitations and disadvantages of conventionaldetection and alarm systems through the provision of improved apparatusfor such purpose.

It is another important object of the invention to provide such improvedapparatus which is particularly adapted for use in environments havingas their only conveniently available source of electrical power astorage battery of considerably higher voltage rating than required foroperation of a Taguchi Gas Sensor but of considerably lower currentdrainage characteristics for continuous operation than would be requiredby a Taguchi Gas Sensor operating at its rated voltage.

It is another important object of the invention to provide suchapparatus employing an audio frequency oscillator, operating in aswitching mode for highest power conversion efficiency, for convertingthe relatively high voltage low current DC. power normally availablefrom a storage battery or the like into an audio frequency output ofsubstantially lower voltage and substantially higher currentcharacteristics for use both in supplying activating power to a TaguchiGas Sensor or comparable sensing instrumentality and in supplying anaudio warning signal to a suitable audio transducer component when thealarm portion of the apparatus is to be operated responsive to sensingof the existence of a hazardous condition by the sensor.

It is another important object of the invention to provide suchapparatus in which the activating circuit for the audio warningcomponent is controlled by an electrically responsive switching devicecoupled with the sensor and including means for delaying actuation ofthe switching device for a suitable period of time to prevent thegeneration of false warning signals upon initial start-up of theoperation of the apparatus.

It is another important object of the invention to provide suchapparatus in which a secondary lower frequency oscillator is employedfor producing a control signal of subaudio frequency, which is coupledwith the main oscillator for causing the output of the latter toalternate between a pair of different audio frequencies in order toprovide an audible warning signal of distinctive dual tonecharacteristics.

Still other important objects of the invention, including certainsignificant details of construction, will be made clear or becomeapparent to those skilled in the art from the accompanying drawing andthe detailed description of a preferred embodiment of the invention thatfollows.

In the drawing, the single FIG. 1 is a schematic diagram of a preferredembodiment of the invention showing the various components andelectrical connections employed in the improved apparatus.

Referring to the drawing, the currently preferred embodiment shown inFIG. 1 broadly includes an electrical power source 10, a systemactivating main power switch 12, a positive polarity supply lead 14, anegative polarity supply lead 16, a hazard condition sensor 18, a mainaudio frequency oscillator 20, an audio warning signal transducer 22, anelectrically controlled switching device 24, control and delay meansbroadly indicated at 26 for coupling the sensor 18 with the switchingdevice 24, and an auxiliary low frequency oscillator broadly indicatedat 28 coupled with the main oscillator 20 for alternating the output ofthe latter between a pair of different audio frequencies.

In the types of applications for which the invention is especiallysuited, the power source 10 will normally be an ordinary electricalstorage battery 30, preferably of the kind having a nominal voltageoutput of 12 volts direct current, in order to provide a convenientsupply source for the various active electronic components of the systemhereinafter described when such components are to be provided throughthe employment of widely available integrated circuit packages and othersolid state devices.

The positive and negative supply leads l4 and 16, including the mainpower switch 12 preferably included in the former, are conventional and,presuming employment of a 12 volt storage battery 30 for the source 10,will provide avenues of connection with such source of 12 voltelectrical operating power for the system. If desired, one of the leads16 may be grounded, as indicated in dotted lines at 32. Those skilled inthe art will appreciate, however, that, by employing different specificsolid state components than those illustrated and used in the preferredembodiment, various electrical polarities could be reversed; and, also,that there is no inherent requirement that the system must be operatedwith either of the leads 14 and 16 at absolute ground potential.

The sensor 18 is preferably a Taguchi Gas Sensor Model T.G.S. 308manufactured by Figaro Engineering, Inc. of Osaka, Japan, and availablein this and other countries through various distributors of suchcompanys products. If and when equivalent devices of domesticmanufacture become available, they could also be employed. The mentionedpresently preferred component for use as the sensor 18, however,internally includes input and output electrode structures schematicallyrepresented in the drawing as coils 34 and 36 respectively coupled witheach other by a zone of variable electrical conductivity representedschematically in the drawing by the space 38 between coils 34 and 36.During operation of the sensor 18 in effective monitoring condition fordetecting the presence of smoke, unburned hydrocarbon gases or the like,the application of an electrical activating potential of approximately 1volt, either AC. or DC, across the terminals of structure 34 isrequired, which serves both to heat the coupling zone or space 38 and toprovide a potential from which the conductivity between the structures34 and 36 may be sensed at the terminals of the structure 36. The sensor18 draws approximately 0.6 Ampere of current when in such standbymonitoring condition and even more when in the conductive state thereofcaused by detection of a hazard condition. When the ambient atmosphereor medium, which is admitted to the zone or space 38, contains evenquite minute quantities of smoke or unburned hydrocarbons, theconductivity between the structures 34 and 36 increases markedly andelectrical current flows therebetween in sensible amount. Although meanshereinafter described are provided for appropriately adjusting (i.e.,limiting) the sensitivity of the apparatus, in order to preventundesired response to a normal atmosphere containing usual amounts ofcigarette smoke or the like, the sensor 18 itself is extremely sensitiveand quick in its response to the presence of any appreciable quantity ofhazard indicating media.

In view of the previously noted relatively high current draincharacteristics of the sensor 18, it will be perceived that operationthereof on a continuous basis from dry cells or the like would be highlyimpractical, not only due to the short life of low voltage batteriesunder such conditions of heavy current drain, but also because, evenwhile there might remain sufficient electrical power for operating thesensor 18 to accomplish a detection, there would not likely besufficient power available or remaining for operation of conventionalalarm or warning devices for any appreciable period of time. It has beenfound, however, that, with the apparatus of this invention, reliable andefficient operation of such systems from an ordinary storage battery canbe achieved by deriving the power for'the sensor 18 (at the voltage andcurrent levels it requires) through the provision of an oscillatorpowered by the battery 30, together with the employment of an audio typealarm or warning signal produced from the same oscillator output used topower the sensor 18 without need for any separate warning generator orany source of additional electrical power for operating the warningportion of the system.

It should be noted that the Taguchi Gas Sensor 18 requires an initialwarming up period, upon activation thereof, during which moisture orgases accumulated in the space 38 during a period of idleness may bepurged therefrom, and in order to permit the temperature of the zone orspace 38 to'stabilize at the desired level to which it is heated duringnormal operation. The period required for this purpose will normally beof the order of about 1 minute. During such warm up and selfpurgingperiod of the sensor 18, it may, however, exhibit a conductive conditionbetween its electrodes 34 and 36, which gives rise to the need for thedelay means incorporated into the control and delay portion 26 of theapparatus of this invention, in order to avoid the occurrence of falsewarning signals as hereinafter more fully explained or the equallyundesirable alternative of having to provide some sort of manualsilencing button that must be held during the warm up and purgingperiod.

The main oscillator 20 is conveniently provided in the preferredembodiment through the use of a Type MFC 8010 integrated circuit package40, which is made and commercially distributed in this and othercountries by the semiconductor products division of the MotorolaCorporation, together with means for providing the desired feedbackpaths and other connections hereinafter described. Such packaged activecomponent 40 used in the oscillator 20 is usually employed in moderatepower audio amplifiers, but, for purposes of this invention, is operatedas a square wave power oscillator functioning in a two state (ratherthan a linear) mode, in order to attain higher efficiency (approachingpercent) in the conversion of direct current electrical power from thesource 10 into lower voltage high usable current power for the sensor 18and other parts of the system yet to be fully described. As employed inthe oscillator 20 of this invention, the component 40 effectivelyconverts 12 volt power from the battery 30 into a square wavealternating current output of approximately 2 volts peak-to-peak atapproximately 0.6 Ampere with a preferred frequency of around 1 to 1.5kilocycles (which it is noted is not only adequate for powering thesensor 18, but also is within the audio portion of the spectrum and inthat range of the latter that is normally most distinctively perceivedby the human ear), and accomplishes such conversion with a current drainon the 12 volt battery 30 of the order of only about 60 milliamperes(due to the low power dissipation of individual active elements of thepackage 40 during half-cycles of the switching mode in which theoscillator 20 is operated).

Since the internal design of the integrated circuit package 40 per sedoes not of itself constitute an aspect claimed in connection with thepresent invention, and since technical data regarding the same isavailable from the manufacturer of such component, it is not deemednecessary to fully describe the internal construction of the package 40.Rather, the limits of the package 40 are indicated in the drawing by adotted line box with the terminals of the package 40 numbered tocorrespond with the terminal reference numbers conventionally associatedwith the commercial component, and the general network of constituentelements within the package 40 is herein schematically indicated in thedrawing without detailed description thereof merely for the possibleconvenience of those skilled in the art who may already be familiar withsuch component package 40, or who will readily grasp the nature thereoffrom the schematic representation included in the drawing. It may behelpful in passing, however, to

note that terminals 7 and l of the package 40 are respectively thepositive and negative supply terminals thereof, which are appropriatelycoupled with the power leads 14 and 16 of the apparatus of thisinvention; that terminal 8 of the package 40 is its output terminal;that terminal 4 of the package 40 is its main input terminal, which isnon-inverting (i.e., a terminal with respect to which an electricalinput wave applied thereto is not inverted in the wave form of theresultant output at terminal 8); and that terminal 3 of the package 40is an inverting input terminal thereof (so that terminals 3 and 4provide for the application to the package 40 of differential inputs).

The oscillator 20 is provided with a negative feedback path and networkand a positive feedback path and network; the negative feedback path istraceable from the output terminal 8 of the package through lead 42,resistance 44 and lead 46 to the inverting input terminal 3 of thepackage 40, with the divider network being completed by lead 48,capacitance 50 and lead 52 coupled with the main negative power lead 16;the positive feedback path is traceable from the output terminal 8 ofthe package 40 through lead 54, resistance 56, lead 58, capacitance 60,lead 62, resistance 64 and lead 66 to the non-inverting input terminal 4of the package 40, with the divider network being completed by aconnection through lead 68 to the midpoint of the voltage dividerpresented by lead 70 coupled to main positive power lead 14, resistance72, lead 74, resistance 76 and lead 78 coupled to the main negativepower lead 16. Terminals 2 and 5 of the package 40 are conventionallybypassed to the negative supply lead 16 through capacitances 80 and 82respectively. Terminal 6 of the package 40 is coupled with the outputterminal 8 through lead 84, a bootstrap pull-up resistance 86, lead 88and the output coupling capacitance 90, it being noted that theresistance 86 thus serves to assure that the pull-up output transistorelements of the package 40 become saturated during positive half-cyclesof the operation of the oscillator 20, as hereinafter explained, therebyassuring minimum internal power dissipation and maximum efficiency ofthe switched mode oscillator 20.

The oscillator 20 functions essentially as follows, it being noted thatthe duty factor thereof is determined by the value ratio of theresistances 72 and 76 of the voltage divider identified above asassociated with the main or non-inverting input terminal 4 of thepackage 40, equal values for the resistances 72 and 76 being preferredin order to establish the DC. potential on input terminal 4 at a levelequal to one-half of the supply voltage existing between leads 14 and16. An output signal voltage at terminal 8 produces a current flow inresistances 56 and 64 of the positive feedback path traced above,thereby changing the voltage potential at the input terminal 4 (ineither direction from the reference potential derived from the supplyvoltage divider 72-76, depending upon the polarity of the output atterminal 8). As the potential at terminal 4 thus is changing,capacitance 50 will charge (or discharge) toward the new potential atterminal 4 through resistance 44 of the negative feedback path tracedabove until the potential at input terminal 3 equals that at inputterminal 4, which will cause the oscillator 20 to commence to switchstates. The positive feedback from the output terminal 8 completes suchswitching and continues the other half-cycle of the operationregeneratively until the opposite extreme of potential differentialbetween the input terminals 3 and 4 is attained (as determined bycomponent and supply voltage values), whereupon discharging (orcharging) of the capacitance 50 will attain momentary equilibrium, thenbe reversed and continued under influence of the feedback to sustain theoscillatory cycling of the oscillator 20.

During such cycling of the oscillator 20, the capacitance 50 alternatelycharges and discharges during successive half-cycles, with the wave formof the potential at terminal 3 essentially in the nature of a saw-toothwave composed of upward and downward exponential ramps extendingalternately above and below the reference potential provided by thedivider 7275 by an amount determined by the maximum potential change ordifferential permitted by component values and the supply voltage.Meanwhile, the wave form of the output at terminal 8 is a square wave ofamplitude varying from a potential of near zero to a positive potentialdetermined by the component parameters and supply voltage, although suchamplitude will preferably be at least somewhat greater than the voltagerequired for excitation of the sensor 18. The frequency of the outputfrom terminal 8 of the package 40 of oscillator 20 is essentiallydetermined by the RC time constant of resistance 44 and the capacitance50 and, of course, by the amount of maximum swing of the voltagedifferential at the input terminals 3 and 4 in relation to the supplyvoltage (since an increased swing will require a longer period for thecapacitance 50 to charge or discharge sufficiently to equalize thepotentials at the terminals 3 and 4 with any given supply voltage,thereby decreasing the frequency of the output, or vice versa). Aspreviously noted, an output frequency of l-1.5 kilocycles is preferredfor the oscillator 20, and an output amplitude of about 2 voltspeak-to-peak is quite suitable for a sensor 18 using a Model T.G.S. 308Taguchi Gas Sensor. As hereinafter more fully explained, the preferredembodiment of the invention contemplates that the output frequency willalternately be switched between two different frequencies, which mayconveniently be near opposite extremes of the above-noted range.

Although the type of oscillator 20 illustrated and described inconnection with the preferred embodiment of the invention is believed toapproach being optimum from the standpoints of functionalcharacteristics in efficiently providing for conversion of DC. powerfrom a storage battery source 30 into an A.C. output adapted both forexciting a Taguchi Gas Sensor and driving an audio warning transducerand of economics as to cost, space requirements and availability ofcomponents, nevertheless, those skilled in the art will appreciate thatspecifically different forms of oscillators could be employed withoutdeparting from the novel and advantageous aspects of the invention, aslong as certain primary particular functional requirements are met(especially the ability to efficiently produce a suitable audiofrequency alternating current output adapted to drive both the sensor 18and the transducer 22 with a minimum of current drain upon powerinitially derived from a relatively higher voltage lower currentdrainage capacity D.C. source such as an ordinary storage battery).

The square wave audio frequency A.C. current output from the oscillator20 is coupled from terminal 8 of IC package 40 through the couplingcapacitance 90 and leads 88 and 92 with one end terminal of anautotransformer 94, the opposite end terminal of which is coupled bylead 96 with the positive supply lead 14. A tap 98 on theautotransformer 94 is coupled with one terminal of the electrode orprimary structure 34 of the sensor 18, and the opposite terminal of theprimary structure 34 is coupled by leads 100 and 96 with the positivesupply lead 14. The tap 98 is appropriately adjusted to apply theexcitation power derived from the output of the oscillator 20 to thesensor 18 at the appropriate voltage for the particular componentemployed as the sensor 18' (about 1 volt for the Model T.G.S. 308Taguchi Gas Sensor). It will be noted that the excitation power from theoscillator 20 for the sensor 18 thus works against or is referred to thepositive supply voltage, since one of the terminals of the structure 34is connected directly to the positive supply lead 14; those skilled inthe art will appreciate, however, that this has been done forconvenience in the preferred embodiment, in the light of the particularcomponents and relationships of the other portions of the overallcircuitry, but that an equivalent reversed polarity version of theapparatus could just as well be employed with appropriate choice ofcomponents and connections.

When the sensor 18 is in a hazard detecting state (i.e., when it issensing the presence of smoke, unburned hydrocarbon gases or the like),the electrical conductivity of the space or zone 38 will increase topermit a flow of current betweenthe electrode structures 34 and 36through an overall path traceable from the positive supply lead 14through leads 96 and 100 to the electrode 34, through the conductivepath created in zone 38 to the electrode 36, through conductors 102 and104 connected to the opposite end terminals of the electrode structure36 and a lead 106 to a connection point 108, thence through asensitivity adjusting potentiometer 110 having an adjustable shortingtap 112, thence through a lead 114, a resistance 116, a lead 118, aresistance 120 and a lead 122 to the negative supply lead 16. The flowof current through the circuit just traced when the sensor 18 isrendered conductive by the detection of a hazard condition creates avoltage potential at the connection point 108, the significance of whichis hereinafter further explained, it being sufficient for presentpurposes merely to note that adjustment of the tap 112 of potentiometer110 permits the voltage potential level at point 108 to be adjusted todifferent values for a given degree of conductivity of the sensor 18,and thereby provides a means of selectively setting the concentration ofhazardous gases that will be required for the sensor 18 to permitsufficient current flow through the last traced circuit to provide apredetermined triggering potential level at the connection point 108.

The audio frequency output from the oscillator 20 is also coupled fromthe terminal 8 of the IC package 40 through the coupling capacitance 90and a lead 124 with the audio frequency transducer 22. With an outputfrom the oscillator 20 of the amplitude being considered in conjunctionwith the preferred embodiment, the transducer 22 may merely consist ofany suitable form of loudspeaker; if desired, however, those skilled inthe art will understand that the transducer 22 could be provided withconventional further audio amplifier means for strengthening the audiosignal to permit driving a larger loudspeaker of a plurality ofloudspeakers.

The terminal of the transducer 22 opposite from the lead 124 is coupledthrough a lead 126, a reset switch 128, a lead 130, the electronicswitching device 24 and a lead 132 with the positive supply lead 14,assuming the conductivity of the switching device 24 under conditionsnext to be discussed. In passing, it is noted that the audio frequencyoutput of the oscillator 20 also works against the positive supplypotential with respect to the output utilization branch incorporatingthe transducer 22, but that those skilled in the art could easilyprovide a reversed polarity equivalent arrangement, if desired.

The electronic switching device 24 of the preferred embodiment is asilicon bilateral solid state switch of the type commonly referred to asa TRIAC, which is characterized by its ability to conduct anode currentat terminal 134 of either polarity with respect to its cathode terminal136 whenever control current has been caused to flow between its gateterminal 138 and its cathode terminal 136. Once so triggered, the TRIACdevice 24 is further characterized by its property of maintaining theconductivity path established between its anode and cathode terminals134 and 136 until the flow of such anode-cathode current has beenexternally interrupted, as by manual operation of the reset switch 128.Accordingly, once the alarm transducer 22 has been activated to audiblyreproduce a signal from the oscillator 20 by virtue of the TRIAC device24 having been triggered into its conductive state, such alarm signalwill be continued until it has been recognized by the user of theapparatus and such user has'cutoff the warning signal and reset theapparatus by momentarily manually opening the reset switch 128. In thepreferred embodiment, it has been found that the Type 40528 TRIAC, madeand distributed in this and other countries by Radio Corporation ofAmerica, operates most satisfactorily, and particularly with respect tothat further attribute of TRIAC switching devices by which they areadapted to maintain their conductive state, once triggered by anappropriate control signal, even though the switched signal appliedthereto is of the AC. type, provided that the transition period of suchsignal from one polarity to the other is sufficiently rapid. In thepreferred embodiment, since the output from the oscillator 20 has asquare wave type wave form, such transition period is so short that noproblem has been encountered, since the minimal transition periodinvolved with such square wave signal is too short to allow the chargecarriers of the TRIAC device 24 to clear.

Thus far, the basic operation and interrelationships of the oscillator20, the excitation power circuit for the sensor 18, the audio warningtransducer 22 and the TRIAC switching device 24' associated with thelatter have been considered; it remains, with respect to the most basicportions of the improved apparatus, to explain the manner in which theTRIAC switching device 24 (and therefore the warning transducer 22) arecontrolled in response to the sensing of a hazard condition by thesensor 18. Then, it will be most appropriate to further consider certainadditional features incorporated into the preferred embodiment forproviding advantageous special functions in the apparatus such as anautomatic delay of any operation of the warning transducer 22 until thesensor 18 has warmed up and become stabilized, the provision of a dualtone warning signal, the provision of simple means for testing theopgated from an operational amplifier (OP AMP) 140 operated in a voltagecomparator mode. The component employed for the comparator 140 in thepreferred embodiment is one-half of a type 1458 dual OP AMP such as madeand distributed in this and other countries by Motorola Corporation, theother half of such component being employed in the auxiliary oscillator28 hereinafter to be described. The terminals of the portion of thecomponent used for the comparator 140 as indicated on the drawing arethose conventionally associated with the various terminals of thecommercial component itself. Due to the commonness of such integratedcircuit packages for providing operational amplifiers, and since theinternal details thereof are both well understood by those skilled inthe art and do not a per se constitute an aspect of the presentinvention, the

circuitry of the preferred embodiment associated with the comparator 140need herein be explained only with reference to the connections made tothe various terminals of the OP AMP component being employed in order tooperate the same in a voltage comparator mode. A DC. reference voltage,preferably equal to about one-third of the supply voltage, is applied toterminal of the comparator 140 by means of a voltage divider includinglead 142, resistance 144, lead 146, and resistance 148 coupled betweenthe supply leads 14 and 16, with a tap lead 150 connecting theintermediate lead 146 of the divider with the terminal 5 of comparator140. It may be noted that the terminal 5 is a non-inverting inputterminal and that the reference voltage applied thereto is compared bythe comparator 140 with any voltage applied to the inverted inputterminal 6 thereof through the lead 152 coupled therewith. The lead 152is connected with the positive supply lead 14 through a connection point154 and a resistance 156, and the connection point 154 is coupled withthe connection point 108 by a diode 158. As long as the voltagepotential at connection point 154 (and therefore at terminal 6 ofcomparator 140) is lower than the reference voltage applied to terminal5 of the comparator 140, the output of the comparator 140 at outputterminal 7 thereof will be maintained near the positive supply voltage.The output from terminal 7 of the comparator 140 is coupled through alead 160, a resistance 162 and a lead 164 with the control element 138of the TRIAC device 24. As long as the output from the comparator 140applied to the control terminal 138 of the switching device 24 remainsnear the positive supply voltage level, the device 24 will not betriggered and will present a nonconductive path or essentially opencircuit between the anode 134 and cathode 136 of the device 24, therebypreventing the warning transducer 22 from responding to and repro ducingthe audio output signal from the oscillator 20. If the voltage potentialat point 154 and terminal 6 of comparator 140 should become morepositive than the reference voltage at terminal 5 of the comparator 140,however, the output of the comparator 140 at terminal 7 thereof willchange to near the negative supply potential thereby causing gatingcurrent to flow through the resistance 162 to the control terminal 138of the TRIAC device 24 thence through the latter to the cathode 136thereof and back through lead 166 to the lead terminal 8 of thecomparator 140. A resistance 168 coupled between the control terminal138 of the TRIAC device 24 and the lead terminal 8 of the comparatorprovides for development of a sufficient potential difference betweenthe control terminal 138 and the cathode 136 of the TRIAC device 24 toassure triggering of the device 24. Whenever the device 24 is thustriggered, the previously traced circuit for operation of the transducer22 will be completed through the conductive path then establishedbetween the anode 134 and the cathode 136 of the switching device 24and, as previously noted, such circuit will be maintained unless anduntil the reset switch 128 is operated, even though the output from thecomparator 140 might thereafter change toward its standby condition (forexample, upon interruption or cessation of a hazard condition beingdetected by the sensor 18). Capacitances and 172 respectively connectedbetween terminals 5 and 6 of the comparator 140 and the negative supplylead 16 serve to by-pass electrically transients from external sourcesto minimize the chances of false triggering of the warning alarmtransducer 22, it being noted that a by-pass capacitance 174 ispreferably provided for similar reasons and connected between the supplyleads l4 and 16 by leads 176 and 178.

As is believed apparent, when a hazard condition is detected by thesensor 18, the positive potential at connection point 108 tends to risedue to conduction between the electrodes 34 and 36 as previouslyexplained; this rise in positive potential at the connection point 108is passed through the diode 158 to connection point 154 and lead 152 tothe terminal 6 of the comparator 140 to bring about triggering of theTRlAC switching device 24 whenever a hazard condition is detected by thesensor 18.

It will be noted, however, that the connection point 154 is also coupledthrough an oppositely facing diode 180 with a connection point 182 thatis in turn coupled with the positive supply lead 14 through a resistance184 and with the negative supply lead 16 through lead 186, capacitance188 and lead 190. Such last mentioned additional circuitry provides aneeded automatic delay against premature triggering of the TRIAC device24 upon initial startup of the apparatus in the following manner. Thevoltage potential at connection point 154, which provides the input toterminal 6 of the comparator 140, can approach the voltage potentialestablished at connection point 108 by the sensor 18 being renderedconductive by detection of a hazard condition only if the voltagepotential stored by the capacitance 188 and appearing at connectionpoint 182 is at least somewhat more positive than the voltage potentialoccurring at the connection point 108. Upon initial start up of thesystem, however, any voltage potential at the connection point 182 willbe very low due to the fact that the capacitance 188 will have beendischarged during any inactive period of the apparatus through a patharound through the resistances 184, 144 and 148. Accordingly, afterinitial start up of the apparatus, sufiicient time must elapse forcurrent flow through the resistance 184 to charge the capacitance 188 sothat the potential at connection point 182 will be at least slightlymore positive than the reference voltage applied to terminal 5 of thecomparator 140; any voltage at connection point 108, no matter howpositive, then can operate to trigger the switching de vice 24. Thevalues of the resistance 184 and capacitance 188 may be chosen toprovide any desired interval for such delay period, a delay of about oneminute being employed in the preferred embodiment.

After the mentioned automatic delay for warm up and stabilization of thesensor 18 after initial start up of the apparatus, an extremelycomprehensive and reliable test of the functional condition of theapparatus may be made by manually opening the test switch 192, which iscoupled in parallel with the resistance 116. It will be observed thatthe switch 192, when not operated to its test position shunts across theresistance 116; however, when the additional resistance of component 116is introduced into the circuit providing impedance from the connectionpoint 108 to the negative supply lead 16 by virtue of opening of thetest switch 192, this will cause the small residual current whichnormally flows through a properly functioning sensor 18 even in itsstandby or non-hazard sensing condition to generate a sufficient voltageacross the resistance 116 to raise the voltage potential at connectionpoint 108 to or above the potential of the reference voltage beingapplied to terminal of comparator 140. When this occurs, the increasedpotential at point 108 is passed to a point 154 and terminal 6 ofcomparator 140 to effect a simulated sensing of a hazard condition bythe sensor 18 and resultant operation of the switching device 24 and thewarning transducer 22, if the oscillator 20 and the various controlcircuits associated with the sensor 18 are properly operating aspreviously described. Note that such test even verifies that operabilityof the automatic delay feature of the control portion of the apparatus,since the test will not produce an affirmative result by way of anaudible signal from the transducer 22 unless or until the delay periodhas elapsed and the sensor 18 achieved operating equilibrium after anystart up of the apparatus. Thus, upon opening the test switch 192 duringnormal standby operation of the apparatus, if an audible warning signalis immediately heard to emanate from the transducer 22 and to continueeven after reclosure of the test switch 192, the user may feel wellassured that the apparatus is properly functioning. After any such test,as after any hazard triggered operation of the alarm portion of theapparatus, the audible warning from the transducer 22 will continueuntil the reset switch 128 is momentarily operated to cutoff anodecurrent to the TRIAC device 24, thus restoring the apparatus to itsnormal standby or monitoring condition.

Also incorporated in the preferred embodiment of the invention is asecondary oscillator also operating in a two state or switch mode toprovide a substantially square wave output therefrom, but such auxiliaryoscillator 28 is arranged to operate at a substantially lower frequencythan the primary oscillator 20, which should be below the audible rangeand preferably may be approximately one cycle per second. The secondaryoscillator 28 employs a conventional OP AMP 194, which is convenientlyprovided by the other half of the dual OP AMP integrated circuit packagethat is used to provide the comparator 140. As indicated in the drawing,the terminals 1, 2, 3 and 4 of the commercial integrated circuit packageare those used in connection with the OP AMP 194 employed in thesecondary oscillator 28. Terminal 4 of the OP AMP 194 is connected tothe negative supply lead 16, while terminal 3 thereof is coupled withthe positive supply terminal through lead 196, resistance 198, leads 66,68 and 74, resistance 72 and lead 70. The terminal 1 of the OP AMP 194is the output terminal of the auxiliary oscillator 28 and varies insquare wave fashion between potential levels respectively near that ofthe negative supply lead 16 and that of the positive potential appliedto the terminal 3. Those skilled in the art will recognize the negativefeedback path for maintaining oscillations in the auxiliary oscillator28 as including leads 204, 202 and 210, resistance 212 and leads 214 and196 leading from the output terminal 1 to the input terminal 3 of theauxiliary oscillator OP AMP 194. The positive feedback path for theauxiliary oscillator 28 is similarly traceable through leads 204, 216,resistance 218 and leads 220 and 222 to the other input terminal 2 ofthe OP AMP 194.

During the half cycle of the oscillatory output of the oscillator 28during which the potential at output terminal l of the OP AMP 194 isrelatively positive, the diode 200 that is coupled with the outputterminal 1 through leads 202 and 204 will be reversely biased, so thatthe positive half cycles of the output from oscillator 28 will notaffect the operation of the primary oscillator 20 in any way. However,during the more negative half cycles of the output from the auxiliaryoscillator 28 the diode 200 will conduct so that current may flowthrough the resistance 206 to a point of connection 208 with thepositive feedback path associated with the primary oscillator 20 duringthe more positive half cycles of the output of the oscillator 20; thisresults in an attenuation of the positive feedback signal from terminal8 to terminal 4 of the IC package 40 of the primary oscillator 20, andthereby a decrease in the magnitude of 7 change of the potential atterminal 4 of package 40 relative to the reference potential normallyapplied thereto. Since the frequency of the primary oscillator 20 isdependent upon the magnitude of such potential change at terminal 4 ofthe package 40, as previously explained, this results in operation ofthe oscillator 20 at a higher audio frequency than its normal frequencyof oscillation during any periods during which the diode 200 is causedto conduct by the output from the auxiliary oscillator 28. Thecapacitance 224 is provided to prevent changes in the D.C. potentialoccurring when diode 200 is conductive from being effectivelytransferred back to the input of the primary oscillator package 40,since a steady state change in such input voltage would tend to causethe duty factor of the primary oscillator 20 to depart from 50 percent(which would be undesirable by tending to reduce the magnitude of theeffective output otherwise available from the primary oscillator 20).

As previously indicated the significant effect of the provision of theauxiliary oscillator 28 is its noted operational effect upon thefrequency of oscillation of the primary oscillator 20 so that the outputof the latter will alternate between two different audio frequencies. Inthe preferred embodiment in which the lower of such frequencies isapproximately 1 kilocycle and the higher of the same approximately 1.5kilocycles, such alternating variation in the frequency of the outputfrom the oscillator 20 has virtually no effect upon the efficientenergization of the sensor 18, but does have the desired result ofproviding an alternating dual tone warning signal from the alarmtransducer 22 which is of such distinctive characteristics as to attractimmediate attention even in otherwise relatively noisy environments.

It may be noted that the following component types and values have beenfound quite satisfactory in the preferred embodiment of the invention:

COMPONENT TYPE 0R VALUE Power source l0 Ordinary l2 volt storage batterySensor 18 Model T.G.S. 308 Taguchi Gas Sensor (Figaro Engineering Co.)Transducer 22 Ordinary permanent magnet loudspeaker, 8 ohms Switchingdevice 24 TRIAC Type 40528 (R.C.A.) IC package 40 Type MFC 8010 audioamplifier module (Motorola) Resistance 44 47K ohms Capacitance 50 .1 mfdResistance 56 22K ohms Capacitance 60 .022 mfd Resistance 64 47K ohmsResistances 72 and 76 4.7K ohms Capacitances 80 and 82 .22 mfdResistance 86 10K ohms Capacitance 90 100 mfd Autotransformer 94 5:1, 2ohms Potentiometer l 10 K ohms Resistance ll6 100K ohms Resistance 120820 ohms lC packages 140 and 194 Type 1458 dual op amp (Motorola)Resistance 144 10K ohms 25 Resistance 148 4.7 ohms Resistance 156 3.3megohms Diodes 158, H and 200 Type lN4l48 Resistance 162 820 ohmsResistance 168 390 ohms Capacitances 170 and l72 .68 mfd Capacitance l74.22 mfd 30 Resistance 184 3.3 megohms Capacitance 190 100 mfd Resistance198 3.3 megohms Resistance 206 22K ohms Resistance 212 l megohmResistance 218- 3.3 megohms Capacitance 224 .l mfd Those skilled in theart will readily appreciate that a number of minor modifications mightbe made from the preferred embodiment shown and described for purposesof illustrating the invention without departing from the true spirit orreal essence of the improvements provided by the invention. For example,different specific commercially available components of equivalentnature could be employed with conventional related alteration ofelectrical polarities, voltage or current values and the like.Accordingly, it is contemplated that the scope of the invention shouldbe fairly deemed to extend not only to the scope of the subject matterdefined by the claims which follow, but also to structural andfunctional equivalents thereof.

1 claim:

1. In electrical detection and alarm apparatus for sensing the presenceof smoke, gas or the like and providing an audible warning thereof,which is adapted for operation with a limited permissible amount ofcontinuous current drain from a supply source of direct currentelectrical power of predetermined voltage such as an electrical storagebattery:

means for sensing the presence of smoke, unburned hydrocarbon gases orthe like,

said sensing means requiring for operation thereof the applicationthereto of electrical energizing power of voltage substantially lowerthan the voltage of said supply source and of current drainsubstantially higher than said permissible amount, said sensing meanshaving sensing terminal means normally characterized by an electricalparameter of predetermined value therebetween, said param eter beingchanged to a different value when said sensing means detects thepresence of smoke, unburned hydrocarbon gases or the like; electricaloscillatory means, coupled with said direct current supply source andderiving operating power from the latter, for providing an alternatingcurrent output of audio frequency and of voltage and currentcharacteristics satisfying said energizing power requirements of saidsensing means;

electrical circuit means for coupling said output of said oscillatorymeans with said sensing means for energizing the latter;

electrically responsive switching means having switched terminal meansand control terminal means;

electrical circuit means for coupling said sensing terminal means ofsaid sensing means with said control terminal means of said switchingmeans for controlling switching operation of said switched terminalmeans of the latter responsive to the value of said parameter;

electrically responsive audio transducer means for providing an audiooutput when an input signal of audio frequency is applied thereto; and

electrical circuit means for coupling the output of said oscillatorymeans with said transducer means through said switches terminal means ofsaid switching means.

2. The invention as set forth in claim 1, wherein is provided asecondary electrical oscillator for providing an alternating currentoutput of substantially lower frequency than said output of saidoscillatory means; and electrical circuit means for coupling saidsecondary oscillator with said oscillatory means for varying thefrequency of said output of the latter between alternate audiofrequencies at a rate alternating at said lower frequency of said outputof said secondary oscillator.

3. The invention as set forth in claim 2, wherein said oscillatory meansincludes a feedback path from the output to an input thereof; and saidoutput of said secondary electrical oscillator is coupled with saidfeedback path.

4. The invention as set forth in claim 2, wherein said output of saidsecondary electrical oscillator is a square wave of sub-audio frequency.

5. The invention as set forth in claim 1, wherein is provided meansfordelaying switching operation of said switching means for apredetermined time following initial activation of said apparatus.

6. The invention as set forth in claim 5, wherein said delaying meansincludes a capacitor coupled through a diode with said circuit means forcoupling said sensing terminal means of said sensing means with saidcontrol terminals of said switching means and oppositely coupled withone pole of said supply source.

7. The invention of claim 1, wherein said switching means includeselectrical components operable to maintain a conductive path throughsaid switched terminals of said switching means once said switchingmeans has been operated and until electrical energization is removedtherefrom.

8. The invention as set forth in claim 1, wherein said circuit means forcoupling said sensing terminal means of said sensing means with saidcontrol terminal means of said switching means includes a voltagecomparator having input terminal means respectively coupled withoscillatory means operates in a switching mode, and said output thereofis substantially a square wave.

12. The invention as set forth in claim 11, wherein is provided meansfor varying the frequency of said output of said oscillatory meansbetween a pair of alternate different audio frequencies at a sub-audiofrequency rate.

1. In electrical detection and alarm apparatus for sensing the presenceof smoke, gas or the like and providing an audible warning thereof,which is adapted for operation with a limited permissible amount ofcontinuous current drain from a supply source of direct currentelectrical power of predetermined voltage such as an electrical storagebattery: means for sensing the presence of smoke, unburned hydrocarbongases or the like, said sensing means requiring for operation thereofthe application thereto of electrical energizing power of voltagesubstantially lower than the voltage of said supply source and ofcurrent drain substantially higher than said permissible amount, saidsensing means having sensing terminal means normally characterized by anelectrical parameter of predetermined value therebetween, said parameterbeing changed to a different value when said sensing means detects thepresence of smoke, unburned hydrocarbon gases or the like; electricaloscillatory means, coupled with said direct current supply source andderiving operating power from the latter, for providing an alternatingcurrent output of audio frequency and of voltage and currentchaRacteristics satisfying said energizing power requirements of saidsensing means; electrical circuit means for coupling said output of saidoscillatory means with said sensing means for energizing the latter;electrically responsive switching means having switched terminal meansand control terminal means; electrical circuit means for coupling saidsensing terminal means of said sensing means with said control terminalmeans of said switching means for controlling switching operation ofsaid switched terminal means of the latter responsive to the value ofsaid parameter; electrically responsive audio transducer means forproviding an audio output when an input signal of audio frequency isapplied thereto; and electrical circuit means for coupling the output ofsaid oscillatory means with said transducer means through said switchesterminal means of said switching means.
 2. The invention as set forth inclaim 1, wherein is provided a secondary electrical oscillator forproviding an alternating current output of substantially lower frequencythan said output of said oscillatory means; and electrical circuit meansfor coupling said secondary oscillator with said oscillatory means forvarying the frequency of said output of the latter between alternateaudio frequencies at a rate alternating at said lower frequency of saidoutput of said secondary oscillator.
 3. The invention as set forth inclaim 2, wherein said oscillatory means includes a feedback path fromthe output to an input thereof; and said output of said secondaryelectrical oscillator is coupled with said feedback path.
 4. Theinvention as set forth in claim 2, wherein said output of said secondaryelectrical oscillator is a square wave of sub-audio frequency.
 5. Theinvention as set forth in claim 1, wherein is provided means fordelaying switching operation of said switching means for a predeterminedtime following initial activation of said apparatus.
 6. The invention asset forth in claim 5, wherein said delaying means includes a capacitorcoupled through a diode with said circuit means for coupling saidsensing terminal means of said sensing means with said control terminalsof said switching means and oppositely coupled with one pole of saidsupply source.
 7. The invention of claim 1, wherein said switching meansincludes electrical components operable to maintain a conductive paththrough said switched terminals of said switching means once saidswitching means has been operated and until electrical energization isremoved therefrom.
 8. The invention as set forth in claim 1, whereinsaid circuit means for coupling said sensing terminal means of saidsensing means with said control terminal means of said switching meansincludes a voltage comparator having input terminal means respectivelycoupled with said sensing terminal means and a reference potentialderived from said power source, and output terminal means coupled withsaid control terminal means of said switching means.
 9. The invention asset forth in claim 1, wherein said sensing means is a Taguchi GasSensor.
 10. The invention as set forth in claim 1, wherein saidswitching means is a TRIAC.
 11. The invention as set forth in claim 1,wherein said oscillatory means operates in a switching mode, and saidoutput thereof is substantially a square wave.
 12. The invention as setforth in claim 11, wherein is provided means for varying the frequencyof said output of said oscillatory means between a pair of alternatedifferent audio frequencies at a sub-audio frequency rate.